Simultaneous multithreading is a processor design that combines hardware multithreading with superscalar processor technology to allow multiple threads to issue instructions each cycle. Unlike other hardware multithreaded architectures, in which only a single hardware context (i.e., thread) is active on any given cycle, SMT permits all thread contexts to simultaneously compete for and share processor resources. Unlike conventional superscalar processors, which suffer from a lack of per-thread instruction-level parallelism, simultaneous multithreading uses multiple threads to compensate for low single-thread. The performance consequence is significantly higher instruction throughput and program speedups on a variety of workloads
The IBM/R6000 Power 5 and 6 architectures support running multiple threads on a single processor. This is possible because of the “Simultaneous Multi-Threading” (SMT) processor design. SMT enables several process threads to coexist on a single physical processor at one time. This technology maximizes the use of otherwise unused processor cycles increasing the overall work throughput (TPT) of the processor.